Random Prebreakdown Discharges in SF6-A Possible Diagnostic Criterion for Particle-Contaminated Conpressed Gas Apparatus

The corona pulse voltage in SF6 gaps, under impulse voltages, is random in value; its randomness is related to the electrode geometry and is influenced by the gas pressure and the rate of rise of the applied voltage. An analytical model is presented whereby the relationships among these quantities are derived. The model predicts for a given electrode geometry at a certain gas pressure the distribution of the corona onset voltage. The results of testing rod- plane SF6 gaps under switching impulses are presented to verify the applicability of the analytical model. By establishing an electrostatic equivalence between rod-plane gaps and conducting particles in GIS, the above analysis could be extended to the latter problem. The possibility of using the present results and analysis to devise a diagnostic test procedure for particle- contaminated GIS is discussed.